Pellet burning fire pit

ABSTRACT

Provided is an apparatus for burning biomass fuel sources, such as a fire pit for burning wood pellets. A fire pit of the present invention may include a burning chamber having a floor and an opening at the top, and a secondary chamber having a bottom, at least one air intake, and at least one air escape. The secondary chamber may be heated by the burning chamber. The at least one air intake may be located near the bottom of the secondary chamber, while the at least one air escape may be located near the top of the burning chamber. In addition, the primary chamber opening may guide flames out of the burning chamber. The secondary chamber may also include a roof which may overhang said burning chamber.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. Nonprovisional patent application Ser. No. 14/187,458, filed Feb. 24, 2014, the entire disclosure of which is hereby incorporated by reference. U.S. Nonprovisional patent application Ser. No. 14/187,458 claims priority from U.S. Provisional Application Ser. No. 61/769,376 filed Feb. 26, 2013 and entitled Pellet Burning Fire Pit.

FIELD OF THE INVENTION

The present invention generally relates to devices for burning fuel. More specifically, the present invention relates to an apparatus for burning biomass fuel sources, such as wood pellets, and/or granules of solid biomass.

BACKGROUND

Wood and other forms of biomass have been used as a heat source, such as for cooking, since virtually the beginning of civilization. However, past systems and devices, such as those employing wood logs and sticks for fuel have had low efficiency and poor heat transfer. When gas became available in the early 1800s, one of the first uses of gas was cooking, as a gas flame is clean and intense, and the cooking level may be easily controlled. However, gas and electric cooking require a sophisticated infrastructure for gas or power delivery, which is not practical in all locations. For example, half of the world's population is still cooking with biomass fires that are slow and inefficient, and which give off hazardous emissions. Wood and coal fire emissions are the cause of millions of premature deaths each year in developing countries.

Pellet burners are advantageous as compared to conventional stick wood burning devices. Such burners typically use a biomass fuel in the form of small pellets which are made from waste from wood processing industries. Wood pellets typically have a heat value of approximately 8300 BTU's per pound. Moreover, wood pellets give off substantially fewer emissions than traditional wood burners while achieving a higher efficiency. Therefore, most pellet burning stoves meet environmental emission standards. Wood pellets are easier to use than traditional sticks and logs, as they are purchased in pellet form and do not require chopping, splitting, or transporting logs. Moreover, because the wood pellets are processed prior to purchase and contain very little moisture, transporting wood pellets does not include the transport of bugs or pathogens associated with logs. Accordingly, home and industrial pellet burners are in wide use. On the other hand, recreational fires, camping fires, and backyard fires using stick wood are inefficient and produce harmful emissions. Replacing these types of wood stick fires with pellet fires would be more efficient as well as reduce emissions and harmful health effects. However, most pellet burning devices require the aid of a fan or blower to accomplish burning, making it difficult to use same without a power source and/or reducing the portability of the devices.

Pellet burners of the prior art include other disadvantages. For example, U.S. Pat. No. 4,471,751 to Hottenroth discloses a stove. The stove includes a primary air chamber and a secondary air chamber in addition to a combustion chamber. Air from the secondary chamber is directed into the combustion chamber via a plurality of air passageways that are located along the height of the combustion chamber. This configuration is inefficient, as secondary air reaching the combustion chamber does not include optimum burning properties. For example, secondary air of varying temperatures enters the combustion chamber. Moreover, the ratio of primary to secondary air is not as efficient as possible.

In other examples, United States Patent Application Publication No. 2007/0137634 to Traeger et al. discloses a pellet-fired cooking apparatus. United States Patent Application Publication No. 2012/0145139 to Deeds discloses a fire pit/barbeque adapted to transition between and enclosed fire pit configuration and an open configuration which serves as a portable barbecue. In addition, United States Patent Application Publication No. 2012/0196232 to Miller discloses a portable fire pit wherein particularly-sized fuel blocks are manually positioned in a square-shaped configuration around ventilation holds provided through the base of the barbecue pit. None of these devices are as efficient as possible as they do not include the introduction of secondary air into a combustion chamber. Therefore, the fuel and flammable gases obtained from the fuel are not allowed to burn to the fullest extent possible.

Accordingly, there exists a need in the art for a pellet burning device that may be used outdoors, such as for recreational, camping, and backyard fires that is as efficient as possible without the aid of a fan or blower. Moreover, the there exists a need for a device which burns as much of the fuel and gases therefrom as possible.

SUMMARY

Provided is a fire pit comprising a burning chamber having a floor and an opening at the top. Also included is a secondary chamber having a bottom, at least one air intake, and at least one air escape. The air escape vents air from the secondary chamber to the burning chamber. The secondary chamber and the burning chamber may share a common wall. Furthermore, the at least one air intake is located in or near the bottom of the secondary chamber. The common wall includes a lower half and an upper half, and the air escape is located in the upper half of the common wall. The primary chamber top opening guides flames out of the burning chamber. In some embodiments of the present invention, the floor may be a grate. The grate may be 53% open to the air beneath the burning chamber. Moreover, in some embodiments of the present invention, the secondary chamber may include a roof, which may overhang a least a portion of the burning chamber, also. The secondary chamber may be located in the burning chamber. In some embodiments, an apparatus of the present invention may be round or cylindrical. Moreover, primary air may enter the burning chamber through the floor, and secondary air may enter the burning chamber though the at least one air escape. In some embodiments the ratio of secondary air intake area to secondary air escape outlet area is 18-41%.

Another embodiment of a fire pit of the present invention includes a burning chamber, the burning chamber having a floor at least partially open to the air below the burning chamber, a top at least partially open to the air above the burning chamber, and at least one wall common to a secondary chamber. The secondary chamber may surround the burning chamber, the secondary chamber including at least one outer wall, a bottom, and a roof. The common wall comprises a lower half, an upper half, and at least one secondary air escape. The lower half of the common wall is solid. Further, the secondary chamber outer wall includes at least one air intake inlet, which is located near the bottom of the secondary chamber, while the upper half of the outer wall is solid. In some embodiments, the fire pit may be cylindrical. In addition, the roof may cover at least a portion of the top of the burning chamber. Moreover, the floor may be 53% open to the bottom of the burning chamber. In many embodiments, the floor of the burning chamber allows primary air into the burning chamber, while the at least one air escape allows secondary air into the burning chamber. In some embodiments, the ratio of secondary air intake area to secondary air escape outlet area is 18-41%.

Yet another embodiment of the present invention includes a burning chamber having a floor which is a grate and a cylindrical inner wall and a secondary chamber that surrounds the burning chamber. The secondary chamber includes the cylindrical inner wall, a cylindrical outer wall, a secondary floor, and a roof. The cylindrical inner wall includes a plurality secondary air escape outlets, which are located near the roof of the secondary chamber. Moreover, the cylindrical outer wall includes a plurality of secondary air intake inlets, which are located near the secondary floor. The grate allows primary air to enter the burning chamber, while the at least one air escape allows secondary air to enter the burning chamber. The ratio of secondary air intake area to secondary air escape outlet area is 18-41%. Moreover, the secondary chamber roof may cover at least a portion of the burning chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view according to one embodiment of a fire pit of the present invention.

FIG. 2 is a perspective view of the bottom, of the fire pit of FIG. 1.

FIG. 3 is a perspective view of the fire pit of FIG. 1 having a front portion of the fire pit removed so as to show air flow and a fire burning in the fire pit.

FIG. 4 is a perspective view of a second embodiment of an apparatus according to one or more examples of embodiments of the present invention.

DETAILED DESCRIPTION

The following is a detailed description of an apparatus 100 for burning biomass fuels (sometimes “apparatus”). One particular use of such an apparatus 100 is as a pellet burning fire pit. For ease of discussion and understanding, the following detailed description may refer to the apparatus as a pellet burning fire pit, or simply a fire pit, and particularly a pellet burning fire pit designed to burn wood pellets. However, it will be appreciated by one skilled in the art that an apparatus 100 of the present invention may be used in any circumstance where a fire is to be made, including, but not limited to, for cooking, recreational fires, camping fires, and backyard fires. Moreover, an apparatus 100 of the present invention may be configured to employ any biomass fuel including but not limited to wood pellets and corn fuels.

Referring to FIG. 1, an apparatus 100 of the present invention is shown. The apparatus 100 includes a burning chamber 102. The burning chamber 102 is at least partially open at its top 104. Accordingly, the burning chamber 102 includes an opening 128 at the top 104. The opening may guide flames out of the burning chamber 102. Moreover, the burning chamber 104 includes a floor 106 at its bottom. As shown in FIG. 11, the floor 106 may be at least partially open to the air below the burning chamber 102. In the preferred embodiment, the floor 106 may be about 53% open to the air below the burning chamber 102, however any configuration may be used without departing from the scope of the invention. Moreover, in the preferred embodiment, the floor 106 may be a grate, as shown in detail in FIG. 2. As one skilled in the art will appreciate, the floor 106 should be configured to prevent fuel, such as wood pellets, from dropping through the floor 106 of the burning chamber 102. However, the floor 106 need not be open to the air below the bunting chamber 102. In such an embodiment, the burning chamber would receive primary air from the opening 128, which will be described in further detail below. Referring again to FIG. 1, the illustrated burning chamber 102 includes at least one common wall 108. The common wall 108 provides a boundary to the burning chamber 102, which in this case is the burning chamber's 102 outer wall.

The common wall 108 also provides a wall or boundary to a secondary chamber 110 or manifold. In the illustrated embodiment, the secondary chamber 110 surrounds the burning chamber 102. However, it will be appreciated that the secondary chamber 110 may be located in any position. For example the secondary chamber 100 may be located inside the burning chamber 102 or beside the burning chamber 102. The secondary chamber 110 may include a roof 120, a bottom 130, and an outer wall 118. It will be understood that in some embodiments, the secondary chamber 100 may not include an outer wall 118 or a roof 120, such as embodiments wherein the secondary chamber 110 is located inside the burning chamber 102. The secondary chamber 110 includes at least one air intake and at least one air escape. The at least one air intake 112 may be located in the bottom 130 of the secondary chamber 110 and/or near the bottom 130 of the secondary chamber 110. In the illustrated embodiment, the secondary chamber 110 bottom 130 is at least partially open to the air below the apparatus 100. Specifically, the floor of the burning chamber 102 may be a grate which is also the bottom 130 of the secondary chamber. Furthermore, in the illustrated embodiment, the secondary chamber 110 includes a plurality of air intake inlets 112 located around the lower perimeter 116 or bottom of the secondary chamber 110 outer wall 118.

Furthermore, the secondary chamber 110 may include at least one air escape. The air escape may be located at the top of said secondary chamber 110 or near the top of said secondary chamber 110. For example, the common wall 108 may include an upper half 132 and a lower half 134 with the air escape located in the upper half. In the illustrated embodiment, the secondary chamber 110 includes a plurality of air escape outlets 114 located around the upper perimeter 117 or top of the common wall 108. However, as one of skill in the art will appreciate, the air escape need not be outlets 114. For example, the secondary chamber 110 may be open at the top, allowing air to escape. In addition, other configurations may be advantageous in embodiments wherein the secondary chamber 110 does not surround the burning chamber 102.

As discussed above, the secondary chamber 110 need not surround the burning chamber 102. For example, the secondary chamber 110 could be located inside the burning chamber 102 or at other locations. However, the secondary chamber 110 should be configured with the burning chamber 102 such that the burning chamber 102 heats the air inside the secondary chamber 110 and such that the air escape allows air from the secondary chamber 110 to contact the air from the burning chamber 102. As mentioned above, in some embodiments, the secondary chamber 110 may include a roof 120. Furthermore, the roof 120 may cover at least a portion of said burning chamber 102, as shown in FIG. 4. As shown in FIGS. 1-4, the preferred embodiment of the apparatus 100 is round or cylindrical. However, as one of skill in the art will appreciate, it is anticipated that many shapes may be used without departing from the scope of the invention, including, but not limited to, an oval, square, or star. In one embodiment, as provided below in Table 1, the apparatus 100 may include a square, outer secondary chamber 110 which surrounds a round, inner burning chamber 102.

Turning to FIG. 2, a view of the apparatus 100 is shown from the bottom. Shown is the secondary chamber 110, including the outer wall 118 having a plurality of air intake inlets 112. Also shown are the burning chamber floor 106 and the secondary chamber 110 bottom 130. In the illustrated embodiment, the burning chamber floor 106 may be at least partially open to the air below the burning chamber 102. Furthermore, in the illustrated embodiment, the secondary chamber 110 bottom 130 may be at least partially open to the air below the secondary chamber 110. For example, the floor 106 and/or bottom 130 may be a grate. In addition, the common wall 108 and plurality of air escape outlets 114 may be seen through the floor 106 of the burning chamber. Also shown in FIG. 3 are the legs 103 of the apparatus. The legs 103 may be included to lift the burning chamber 102 floor 106 and secondary chamber 110 bottom 130 such that air beneath the apparatus 100 may flow into one or both chambers 102, 110.

Referring to FIG. 3, the illustrated configuration allows primary air 122 to enter the burning chamber 102 through the openings in the floor 106. However, it is anticipated that primary air 122 may also be introduced to the burning chamber 102 through the opening 128 at the top 104 of the burning chamber 102. This may be the case in embodiments wherein the burning chamber 102 floor 106 is not at least partially open to the air below the apparatus and in embodiments having a floor 106 including at least one opening. As discussed above, the apparatus 100 may include legs 103 to elevate the burning chamber 102 and floor 106.

Moreover, the at least one air escape, which may be one or more air escape outlets 114, allows secondary air 124 to enter the burning chamber 102. As will be discussed in further detail below, the secondary air 124 may enter the secondary chamber 110 through the at least one air intake 112, the secondary chamber 110 bottom 130, or both. In preferred embodiments, discussed in further detail below, the ratio of secondary air intake area, including the area of air intake inlets 112 and the open bottom 106 beneath the secondary chamber 110, to secondary air escape outlet area is 18-41%, although any ratio may be employed. Moreover, the ratio may vary depending on the amount of fuel 135 in the burning chamber 102.

Referring again to FIG. 3, primary air 122 enters the burning chamber 102, such as through the floor 106 and/or opening 128. In certain embodiments of the apparatus 100, an initial fire will be started with starter fluid, waxy wood fire starters, or similar methods. In the preferred embodiment, primary air 122 for the fire then enters the burning chamber 102 through the openings in the floor 106, which as discussed above may be a grate. Together, the primary air 122 and fuel 135 cause primary combustion. In addition, secondary air 124 may enter the secondary chamber 110, such as through the one or more air intake inlets 112 or through other means, including but not limited to, an open top. As the secondary air 124 is in the secondary chamber 110, it is heated from the combustion taking place in the burning chamber 102. As the secondary air 124 is heated, it rises upward in the secondary chamber 110. The secondary air 124 is then released into the burning chamber 102, such as through the air escape outlets 114 located near the top perimeter 117 of the inner wall 108.

When the secondary air 124 enters the burning chamber 102, it meets the fuel gases, such as pyrolyzed gases, that were not burned during the primary combustion with the primary air 122. The secondary air 124 is fresh air which is full of oxygen and has been heated to a high temperature. Accordingly, when the secondary air 124 meets the fuel gases, the secondary air 124 ignites the fuel gases. In this way, a very efficient burning of the fuel source takes place, as fuel gases which may undergo combustion are not wasted. Moreover, as the air escape outlets 114 are located near the top of the inner wall 108, the flame caused by the secondary air 124 is at the top of the burning chamber 102. Furthermore, the opening 128 at the top of the burning chamber 102 may direct the flame out of the burning chamber 102. Therefore, the flames can be both felt and seen by a user. In addition, the apparatus 100 may operate employing natural airflow only. As one of skill in the art will appreciate, as the burning chamber 102 heats, the amount of secondary air 124 flowing through the secondary chamber 110 will increase. Therefore, heat output is increased. Moreover, the above-described configuration provides for air flow and flames 126 that primarily move upward, as shown in FIG. 3. As discussed above, in addition to the secondary air 124 provided from the secondary chamber 110 and air escape outlets 114, a portion of the secondary air 124 may also be provided in the same way as the primary air 122, flowing through the floor 106 of the burning chamber 102.

The user may regulate the amount of heat by adjusting the amount of fuel in the apparatus 100, such as by adding wood pellets at the top of the burning chamber 102. Moreover, the amount of heat may be controlled by the quantity and size of air intake inlets 112 and air escape outlets 114, thereby regulating the flow of secondary air 124. As provided above, in a preferred embodiment, the inlets 112 and outlets 114, as well as the grated floor beneath the entire apparatus 100, are configured such that the ratio of secondary air intake area to secondary air escape outlet area is 18-41%. Moreover, in some embodiments, the roof 120 of the secondary chamber 110 may have a slight overhang 136 so as to cover a portion of the burning chamber 102, as shown in FIG. 3. This configuration prevents the secondary air 124 from rising upward out of the burning chamber 102 too quickly and also provides a down flow of air from wind. Accordingly, the flames may be further directed upward from the apparatus 100, to produce an even more aesthetically pleasing fire and flames. In one embodiment of the present invention 100,000 BTUs of energy are released in an hour with about thirteen pounds of wood pellets burned. Unspent fuel, or ash, falls through the openings in the floor 106 to surface below when an embodiment having an open floor is employed.

Turning to FIG. 4, a second embodiment of an apparatus 100 of the present invention is shown. The apparatus 100 includes a cover or cone 138. Although the cone 138 is not necessary for operation of the apparatus 100, it further directs flames 126 upward and out of the apparatus 100. Such a cone 138 may be particularly advantageous in windy conditions. It is anticipated that the cone 138, if used, may be an add-on or attachment to the apparatus 100, which may be used and removed as desired by the user. Of course, one of skill in the art will appreciate that the con 138 may also be a permanent feature of the apparatus 100. In addition, the apparatus 100 need not include a cone 138 to create flames 126.

An apparatus 100 of the present invention provides a number of benefits, including, but not limited to, letting off very little smoke, being portable, requiring no power, burning wood pellets with low ash content after burning, and producing an aesthetically pleasing flame. Moreover, the configuration of the apparatus 100 provides for efficient burning of wood pellets in the burning chamber 102. Moreover, an apparatus 100 of the present invention may operate on natural air flow only. Accordingly, it is not necessary to utilize a fan or a blower, which provides for portability and eliminates the need for a power source. An apparatus 100 of the present invention also produces very low particulate emission levels and little airborne fly ash. The combustion air flow is naturally varied according to beat output.

Table 1 below provides dimensions for a number of exemplary preferred embodiments of an apparatus 100 of the present invention of various sizes, with the medium embodiment being most preferred. It should be understood that the embodiments below are provided for purposes of illustration only and are not intended to be limiting. It is anticipated that one skilled in the art could vary any of the dimensions without departing from the scope of the invention.

TABLE 1 (all dimesions in inches, square inches, or cubic inches as appropriate): Square Outer Large Medium Square Round Round Round Outer Inner Large with Medium with Round with Round Cone Round Cone Small Small Inner Cone Outside 19.00 19.00 13.50 13.50 6.00 6.00 9.00 9.00 Diameter Out Radius 9.50 9.50 6.75 6.75 3.00 3.00 4.50 4.50 Inside 17.00 17.00 12.00 12.00 5.00 5.00 7.75 7.75 Diameter without Lip Inside Radius 8.50 8.50 6.00 6.00 2.50 2.50 3.88 3.88 without Lip Inside Radius 16.50 13.25 11.13 8.13 5.38 5.38 7.75 5.13 Inside 8.25 6.63 5.56 4.06 2.69 2.69 3.88 2.56 Diameter with Lip Bottom Grate 0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53 Open to the Air Below Air Escape 0.44 0.44 0.44 0.44 0.38 0.38 0.44 0.44 Size Air Intake 0.22 0.22 0.22 0.22 0.19 0.19 0.22 0.22 Size Number of 80.00 80.00 55.00 55.00 30.00 30.00 38.00 38.00 Secondary Air Intakes Number of 71.00 71.00 50.00 50.00 25.00 25.00 32.00 32.00 Secondary Air Outlets Height of 8.00 8.00 7.00 7.00 3.50 3.50 6.00 6.00 Apparatus Sides Height of 8.00 8.00 7.00 7.00 2.50 2.50 6.00 6.00 Apparatus from Ground Burn Rate in 26.00 26.00 13.00 12.00 4.00 4.00 6.00 5.00 Pounds per Hour Volume 9068.32 9068.32 4005.86 4005.86 282.60 282.60 1526.04 1526.04 Under the Apparatus to the Ground Whole 566.77 566.77 286.13 286.13 56.52 56.52 127.17 127.17 Bottom Area (Both chambers) Whole 300.39 300.39 151.65 151.65 29.96 29.96 67.40 67.40 Bottom Area × 0.53 Whole Area 453.73 453.73 226.08 226.08 39.25 39.25 94.30 94.30 of Bottom of Primary Chamber Whole Area 240.48 240.48 119.82 119.82 20.80 20.80 49.98 49.98 of Bottom of Primary Chamber × 53% Whole Area 113.04 113.04 60.05 60.05 17.27 17.27 32.87 32.87 of Bottom of Secondary Chamber Whole Area 59.91 59.91 31.83 31.83 9.15 9.15 17.42 17.42 of Bottom of Secondary Chamber × 53% Area of 12.02 12.02 8.26 8.26 3.31 3.31 5.71 5.71 Secondary Air Intakes Area of 10.67 10.67 7.51 7.51 2.76 2.76 4.81 4.81 Secondary Air Escapes Total 70.58 70.58 39.34 39.34 11.91 11.91 22.23 22.23 Secondary Combustion Total Air 213.72 137.82 97.16 51.82 22.68 22.68 47.15 20.62 Output Total Air 311.06 311.06 159.16 159.16 32.72 32.72 72.21 72.21 Input Total Sec 71.93 71.93 40.09 40.09 12.46 12.46 23.13 23.13 Comb Input Area Secondary 15.85 15.85 17.73 17.73 31.76 31.76 24.53 24.53 Chamber Air Input Comb to Burning Chamber Input (%) Secondary 15.11 15.11 19.10 19.10 23.17 23.17 21.63 21.63 Chamber Output to Secondary Chamber Input % Secondary 33.66 52.19 41.27 77.36 54.96 54.96 49.06 112.19 Combustion to Percentage of Output Whole Floor 96.57 96.57 95.28 95.28 91.56 91.56 93.34 93.34 and Bottom Percentage of Total Input Secondary 3.86 3.86 5.19 5.19 10.12 10.12 7.91 7.91 Air Intake Percentage of Total Input Secondary 33.66 52.19 41.27 77.36 54.96 54.96 49.06 112.19 Chamber % of Output Total input to 1.46 2.26 1.64 3.07 1.44 1.44 1.53 3.50 Output Whole Area 3.31 3.31 3.79 3.76 10.60 10.60 0.04 0.04 Under Bottom of the Apparatus. Height from Ground. Height of 42.11 42.11 51.85 51.85 58.33 58.33 0.67 0.67 Side to Diameter Total 2267.08 2267.08 1001.46 1001.46 98.91 98.91 381.51 381.51 Volume of Apparatus Volume of 1814.92 1814.92 791.28 791.28 68.69 68.69 282.89 282.89 Burning Chamber Volume of 452.16 452.16 210.18 210.18 30.22 30.22 98.62 98.62 Secondary Chamber Secondary 24.91 24.91 26.56 26.56 44.00 44.00 34.86 34.86 Chamber to Burning Chamber (%) Wall 1.00 1.00 0.75 0.75 0.50 0.50 0.63 0.63 thickness Volume of 19.94 19.94 20.99 20.99 30.56 30.56 25.85 25.85 Secondary Chamber/ Total Volume Volume of 80.06 80.06 79.01 79.01 69.44 69.44 74.15 74.15 Burning Chamber/ Total Volume Pounds of air 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 for best combustion Pounds of 26.00 26.00 13.00 11.00 4.00 4.00 6.00 5.00 wood pellets per hour Pounds/Hour 260.00 260.00 130.00 110.00 40.00 40.00 60.00 50.00 of air 70 degrees 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 Fahrenheit cu/ft/hr 3470.37 3470.37 1735.18 1468.23 533.90 533.90 800.85 667.38 cu/ft/min 57.84 57.84 28.92 24.47 8.90 8.90 13.35 11.12 cu/ft/sec 0.96 0.96 0.48 0.41 0.15 0.15 0.22 0.19 cu/in/sec 1665.78 1665.78 832.89 704.75 256.27 256.27 384.41 320.34 Pri comb in/ 6.93 6.93 6.95 5.88 12.32 12.32 7.69 6.41 Secondary 23.60 23.60 21.17 17.91 21.51 21.51 17.29 14.41 Combustion Pounds of air 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 for best combustion Pounds of 26.00 26.00 13.00 11.00 4.00 4.00 6.00 5.00 wood pellets per hour Pounds/Hour 260.00 260.00 130.00 110.00 40.00 40.00 60.00 50.00 of air 300 degress 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 Fahrenheit cu/ft/hr 4977.03 4977.03 2488.51 2105.67 765.70 765.70 1148.55 957.12 cu/ft/min 82.95 82.95 41.18 35.09 12.76 12.76 19.14 15.95 cu/ft/sec 1.38 1.38 0.69 0.58 0.21 0.21 0.32 0.27 cu/in/sec 2388.97 2388.97 1194.49 1010.72 367.5.3 367.53 551.30 459.42 Pri comb 9.93 9.93 9.97 8.44 17.67 17.67 11.03 9.19 Secondary 33.85 33.85 30.36 25.69 30.85 30.85 24.80 20.67 Combustion Pounds of air 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 for best combustion Pounds of 26.00 26.00 13.00 11.00 4.00 4.00 6.00 5.00 wood pellets per hour Pounds/Hour 260.00 260.00 130.00 110.00 40.00 40.00 60.00 50.00 of air 600 degrees 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 Fahrenheit cu/ft/hr 7115.49 7115.49 3557.74 3010.40 1094.69 1094.69 1642.04 1368.36 cu/ft/min 118.59 118.59 59.30 50.17 18.24 18.24 27.37 22.81 cu/ft/sec 1.98 1.98 0.99 0.84 0.30 0.30 0.46 0.38 cu/in/sec 3415.44 3415.44 1707.72 1444.99 525.45 525.45 788.18 656.81 Pri comb 14.20 14.20 14.25 12.06 25.26 25.26 15.77 13.14 Secondary 48.39 48.39 43.41 36.73 44.11 44.11 35.46 29.55 Combustion Pounds of air 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 for best combustion Pounds of 26.00 26.00 13.00 11.00 4.00 4.00 6.00 5.00 wood pellets per hour Pounds/Hour 260.00 260.00 130.00 110.00 40.00 40.00 60.00 50.00 of air 1000 degrees 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 Fahrenheit cu/ft/hr 9569.38 9569.38 4784.69 4048.58 1472.21 1472.21 2208.32 1840.26 cu/ft/min 159.49 159.49 79.74 67.48 24.54 24.54 36.81 30.67 cu/ft/sec 2.66 2.66 1.33 1.12 0.41 0.41 0.61 0.51 cu/in/sec 4593.30 4593.30 2296.65 1943.32 706.66 706.66 1059.99 883.33 Pri comb 19.10 19.10 19.17 16.22 33.97 33.97 21.21 17.67 Secondery 21.49 33.33 23.64 37.50 31.16 31.16 22.48 42.84 Combustion Total Air In 35.70 47.53 37.89 49.56 56.42 56.42 38.25 55.98 Per Second at Burning Temperature Sec percent 60.21 70.17 62.39 75.67 55.23 55.23 58.77 76.53 @1000 Primary 39.79 29.88 37.61 24.33 44.77 44.77 41.23 23.47 Combustion at 600 Degrees Total Output 213.72 137.82 97.16 51.82 22.68 22.68 47.15 20.62 Area Air In Per 21.49 33.33 23.64 37.50 31.16 31.16 22.48 42.84 Second Flowing through Air Escapes Secondary 12.94 23.37 14.75 28.37 17.21 17.21 13.21 32.78 Chamber Air in Per Second at Burning Temperature Primary 8.55 9.96 8.89 9.12 13.95 13.95 9.27 10.06 Chamber Air In Per Second at Burning Temperature

Although various representative embodiments of this invention have been described above with a certain degree of particularity, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of the inventive subject matter set forth in the specification and claims. Joinder references (e.g. attached, adhered, joined) are to be construed broadly and may include intermediate members between a connection of elements and relative movement between elements. As such, joinder references do not necessarily infer that two elements are directly connected and in fixed relation to each other. Moreover, network connection references are to be construed broadly and may include intermediate members or devices between a network connection of elements. As such, network connection references do not necessarily infer that two elements are in direct communication with each other. In some instances, in methodologies directly or indirectly set forth herein, various steps and operations are described in one possible order of operation, but those skilled in the art will recognize that steps and operations may be rearranged, replaced, or eliminated without necessarily departing from the spirit and scope of the present invention. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not limiting. Changes in detail or structure may be made without departing from the spirit of the invention as defined in the appended claims.

Although the present invention has been described with reference to the embodiments outlined above, various alternatives, modifications, variations, improvements and/or substantial equivalents, whether known or that are or may be presently foreseen, may become apparent to those having at least ordinary skill in the art, Listing the steps of a method in a certain order does not constitute any limitation on the order of the steps of the method. Accordingly, the embodiments of the invention set forth above are intended to be illustrative, not limiting. Persons skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. Therefore, the invention is intended to embrace all known or earlier developed alternatives, modifications, variations, improvements, and/or substantial equivalents. 

1. A fire pit comprising: a burning chamber, said burning chamber having a floor, and an opening at the top, said opening open to outside air surrounding said fire pit; a secondary chamber having a bottom, at least one air intake, a roof, and at least one air escape, said at least one air escape venting air from said secondary chamber to said burning chamber and said roof including an overhang, said overhang covering a portion of said burning chamber above said at least one air escape; said secondary chamber heated by said burning chamber; said at least one air intake located near said bottom of said secondary chamber; said at least one air escape located near the top of said burning chamber; and said opening configured, to allow flames out of said burning chamber, said flames extending above said fire pit; wherein said overhang is at least partially conical and has an inner edge that is continuous; and wherein said overhang is configured to slow the rise of air from said secondary chamber.
 2. The fire pit of claim 1, wherein said floor comprises a grate.
 3. The fire pit of claim 2, wherein said grate is 53% open to the air below said burning chamber.
 4. The fire pit of claim 1 wherein said burning chamber and said secondary chamber further comprise a common wall.
 5. The fire pit of claim 4 wherein said common wall includes an upper half and a lower half and said at least one air escape outlet is located in said upper half.
 6. The fire pit of claim 1 wherein said overhang is further configured to direct said flames upward out of said fire pit.
 7. The fire pit of claim 1 wherein the shape of said fire pit is selected from the group consisting of cylindrical, oval, square, or star.
 8. The fire pit of claim 1 wherein: said floor allows primary air to enter said burning chamber; said at least one air escape allows secondary air to enter said burning chamber; and a ratio of air intake area to air escape area is 18-41%.
 9. The fire pit of claim 1 wherein said fire pit produces said flames using natural airflow only.
 10. A fire pit comprising: a floor at least partially open to the air below said fire pit and having a burning chamber air opening; a burning chamber, said burning chamber having a top at least partially open to outside air above said fire pit, and at least one wall common to a secondary chamber; said secondary chamber surrounding said burning chamber, said secondary chamber comprising at least one outer wall, a bottom, and a roof including an overhang, said overhang covering a portion of said burning chamber above at least one secondary air escape; said at least one wall common to said burning and secondary chambers comprising a lower half, an upper half, and said at least one secondary air escape; said lower half of said common wall is solid; said at least one outer wall comprising a lower half, an upper half and at least one secondary air intake; said upper half of said outer wall is solid; wherein the cross section of the burning chamber air opening amounts to at least thirty percent of the surface area of the floor; wherein said fire pit is configured to produce flames that extend above said fire pit; wherein said fire pit is not covered by a container used for cooking; wherein said overhang is at least partially conical and has an inner edge that is continuous; and wherein said overhang is configured to slow the rise of air from said secondary chamber.
 11. The fire pit of claim 10 wherein said fire pit is cylindrical.
 12. The fire pit of claim 10 wherein said floor is 53% open to air below said burning chamber.
 13. The fire pit of claim 10 wherein said roof covers at least a portion of said burning chamber.
 14. The fire pit of claim 10 wherein: said floor allows primary air to enter said burning chamber; and said at least one secondary air escape allows secondary air to enter said burning chamber.
 15. The fire pit of claim 14 wherein a ratio of secondary air intake area to secondary air escape area is 18-41%.
 16. An apparatus comprising: a floor comprising a grate and having a burning chamber air opening; a burning chamber, said burning chamber having at least one inner wall and an opening, said opening directly open to outside air above said apparatus; a secondary chamber surrounding said burning chamber, said secondary chamber comprising said at least one inner wall, at least one outer wall, a floor, and a roof including an overhang partially covering said burning chamber above a plurality of secondary air escape outlets; said at least one inner wall comprising said plurality of secondary air escape outlets located in an upper half of said inner wall; said at least one inner wall further comprising a lower half, said lower half of said inner wall is solid; said at least one outer wall comprising a plurality of secondary air intake inlets, said secondary air intake inlets located in a lower half of said outer wall; said outer wall further comprising an upper half, said upper half of said outer wall is solid; said grate allowing primary air to enter said burning chamber; said air intake inlets configured to allow secondary air to enter said secondary chamber; said air escape outlets configured to allow said secondary air to move from said secondary chamber to said burning chamber; wherein the cross section of the burning chamber air opening amounts to at least sixty-nine percent of the surface area of the grate; wherein said fire pit produces a flame that extends above said fire pit; wherein said fire pit is not covered by a container used for cooking; wherein said overhang is at least partially conical and has an inner edge that is continuous; and wherein said overhang is configured to slow the rise of air from said secondary chamber and direct said flame upward out of said fire pit. 